Sound recording



Aug. 9, 1938. E. D. COOK 2,125,890

SOUND RECORDING Filed June 2'7, 19-56 ZSmaentor .Ellaworth D. Cooii (Ittorneg Patented Aug. 9, 1938 PATENT OFFICE SOUND RECORDING Ellsworth D. Cock, Scotia, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 27, 1936, Serial No. 87,618

6 Claims.

This invention relates to a novel method of apparatus for sound recording and more particularly to a novel method and apparatus for producing photo-phonographic sound records with 5 ground noise reduction.

Some of the older type photographic sound records had a large unused clear portion wherein approximately half of the sound track was left clear at no modulation. This resulted in unde- 10 sired sounds when reproduced due to the unexposed but developed silver grains in the clear area of the film and also due to dust, dirt, scratches, etc. on the film. In order to avoid this noise, which is generally referred to as 15 ground noise, it was proposed in Robinson Patent 1,854,159 to shift the axis of the sound track so as to blacken all but the used portion of the positive sound track. In McDowell Patent 1,855,- 197 it was proposed to accomplish this blacking 20 of the positive sound track by interposing a shutter between the recording galvanometer and the film to prevent exposure of the unused portion of the negative film and thereby cause a corresponding blackening of the positive film.

It was proposed in Dimmick Patent 1,999,721 to apply ground noise reduction to a bilaterally modulated sound track and Dimmick preferred to use a multiplex sound track. In the present invention the sound track produced is somewhat 39 similar in appearance to a single section of the, Dimmick sound track but differs therefrom in that instead of the outer envelope of the sound track being changed in width in accordance with the volume an axial masking track'is provided 35 which functions ina manner similar to the McDowell masking track.

One object of the invention is to produce an anti-ground noise sound track without the use of a rectifier or low pass filter circuit.

40 Another object of my invention is to provide a sound track which may be printed either with or without ground noise reduction.

Another object of my invention is to provide simplified records for producing anti-ground noise sound track.

Another object of my invention is to provide an optical means for producing a record corresponding to the envelope of the sound waves.

50 Further objects of my invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which Figure 1 is a schematic illustration of a record- 65 or according to my invention,

Figure 2 is an enlarged View of the sound record as recorded,

Figure 3 is an enlarged view of the masking record as recorded, and

Figure 4 is an enlarged view of a positive print 5 corresponding to Figs. 2 and 3.

Referring first to Figure 1, l indicates the exciter lamp, the light from which is focused by the lens ll upon the galvanometer mirror after passing through the aperture plate l2 which is provided With apertures I3A, B and C, the di mensions of which are determined as hereinafter described. Light passing through the aperture I3A passes through the lens l4 onto the mirror l5 of the galvanometer I6 since it is reflected through the lens [4 to the lens H. The focal length of the lens I4 is so chosen that images 13a, 13b and I30 of the apertures I3A, !3B and 13C are thrown on the slit plate It which is provided with a narrow slit l9 and a wider slit I9. Lens ll focuses image of filament at mirror 55 on to objective lens 2|. Ihe light passing through the slits l9 and I9 is focused on the film 20 by a lens 2|. The slit I 9 is made of such a width that the image thereof on the film 2D is of the order of 1001" or less in order that sound waves of sufficiently high frequency may be properly record-- ed as indicated at 22.

. It will be apparent that the light passing through the slit I9 will be imaged on the film as a fine line varying in length according to the position of the triangular spot I3a on. the slit as the galvanometer mirror I5 is vibrated around the horizontal axis. The triangular spot will move up and down across the slit 19 in accordance with the sound waves thereby producing a sound rec- 0rd such as that shown in Fig. 2 wherein the upper portion represents sounds of a high amplitude and low frequency while the lower portion represents sounds of a lower amplitude and a higher frequency.

The heighth of the aperture I9 is so chosen that the image thereof on the film 20 is one wave length of the lowest sound frequency to be recorded. It will be apparent that as the mirror I5 is oscillated by the galvanometer IS the images l3b and l3c will be moved vertically across this slit l9 and will produce arecord such as shown in Fig. 3 which is complementary to the record shown in Fig. 2. This record as distin- 5 guished from the record of Fig. 2 does not correspond with the individual sound waves but corresponds only with the envelope of the sound waves due to the width of the slit l9. The amplifier, of course, either will be so constructed as to pass no frequencies below the frequency corresponding to the width of the slit H! or will be provided with a filter circuit cutting off the lower frequencies.

The comparison of Figs. 2 and 3 will show that the interior envelope of the record of Fig. 2 corresponds with the transparent portion of the record of Fig. 3. When the record of Fig. 2 is printed onto a positive film it will produce blackened sound records at the outer margins of the sound track as indicated at 2| and 22 in Fig, 4 leaving the portion corresponding to the blackened portion in Fig. 2 clear. If the record of Fig. 3 is then printed on this positive sound track it will produce a blackened center portion 23 corresponding to the internal envelope of the sound record and thus prevent the transmission of light by the unused portions of the film. It

will be apparent to those skilled in the art that it is not necessary for me to run the positive film through the printer twice in order to produce the record of Fig. 4 but that I can superpose the images, 22 and 23 optically and thereby produce the record of Fig. 4 at a single printing operation. It will further be apparent that instead of producing these two records laterally adjacent on a single film I may produce them in the'same lateral position on two separate films thereby permitting me to perform the printing operation without any lateral adjustment of the film in the printer.

It may be desirable, in some instances, as, for example, if the film is of low sensitivity, to use a higher exposure on the masking track than on the sound wave track. This might be accomplished, for example, by using a light absorbing glass or a partially exposed photographic emulsion and correspondingly increasing the light intensity.

If it were desired to print a negative instead of a positive sound track from the combined printing of the negatives of Fig. 2 and Fig. 3 the aperture for the masking track would be made to increase with the space between the apertures [3B and I3C, in which case the masking track would correspond with the exterior envelope of the sound track of Fig. 2 and the composite print would be a corresponding negative from which positive sound records could be subsequently printed.

Having now described my invention, I claim:

1. Sound recording apparatus including means for producing a substantially triangular beam of light, means for producing two beams of light complementary to the sides of said triangle,

means for vibrating all of said beams in accordance with sound waves, means for selecting a narrow portion of said triangular beam and. for selecting portions of said complementary beams corresponding in width with the wave length of the lowest frequency to be recorded and means for directing said selected portions onto a photographic record surface.

2. Apparatus for producing a record of the envelope of sound waves comprising means for directing upon a record surface a beam of light having a width in the direction of motion of the said surface corresponding to one wave length of the lowest sound frequency of which the envelope is to be recorded, and means for vibrating said beam of light transversely of the record surface in accordance with the sound vibrations.

3. The method of making a record of the envelope of sound vibrations comprising the steps of directing onto a record surface a beam of light having one dimension corresponding to one wave length of the lowest sound vibrations whose envelope is to be recorded, vibrating said beam in a direction perpendicular to said first direction in accordance with the sound waves, and moving the record surface along the said first direction at an appropriate speed.

4. Electrical impulse recording apparatus including means providing a light slit having relatively wide and narrow portions, means for directing a light beam on the relatively narrow portion of said slit, means for directing on said relatively wide portion a light beam which is complementary to a side of said first mentioned beam, and means for vibrating said beam in accordance with said impulses.

5. Electrical impulse recording apparatus including means providing a light slit having relatively wide and narrow portions, means for directing a triangular light beam on said relatively narrow portion, means for directing on said relatively wide portion a pair of light beams complementary to the sides of said triangular beams, and means for vibrating said beams in accordance with said impulses.

6. Electrical impulse recording apparatus including means providing a light slit having alined relatively wide and narrow portions, means for directing a light beam on the relatively narrow portion of said slit, means for directing on said relatively wide portion a light beam which is complementary to a side of said first mentioned beam, and means for vibrating said beams in accordance with said impulses.

ELLSWORTH D. COOK. 

